Social structure and spatial-use in a group-living lizard, Cordylus cataphractus

[摘要] ENGLISH ABSTRACT: There is overwhelming evidence that the Armadillo Lizard, Cordyluscataphractus, forms permanent aggregations, and that termites arepossibly the most important component of the diet of this species. Inaddition, the spinose morphology and defensive tail-biting behaviourdisplayed by this lizard species strongly imply that individuals move awayfrom the crevice, where they are more vulnerable to predation. Thereforethe aim of this part of the study was to investigate whether C.cataphractus harvest termites at the termite foraging ports and to discussthe likely ecological implications of termitophagy for this species. Aquadrate at the Graafwater study site, including several crevices housingC. cataphractus groups, was measured out. All the foraging ports of thesubterranean harvester termite (Microhodotermes viator) present in thequadrate, were located and their positions recorded in respect to thedistance from the nearest crevice housing lizards. The presence of C.cataphractus tracks at the foraging ports was used to verify whetherindividuals visited specific termite foraging ports. Tracks were found atforaging ports located at an average distance of 6.1 m, but were alsolocated at foraging ports up to 20 m from the nearest crevice. The resultsstrongly support the hypothesis that C. cataphractus individuals moveaway from the crevice to feed on termites. Termitophagy and the heavyarmature of C. cataphractus appear to be key factors in the group-livingbehaviour of this species. Termitophagy allows individuals to live ingroups as competition for food at the home crevice will be limited. Theheavy armature of C. cataphractus renders it clumsy and slow-moving,compared to other cordylids. Group-living will, however, eliminate juveniledispersal and mate-searching excursions, activities which, in the light ofthe heavy morphology of the species, may result in high predation impact.The global objective of the study was to investigate social structure andspace-use in Cordylus cataphractus. For the correct interpretation of dataon the latter, it was necessary to first establish an ethogram for the studyanimal. Members of a multi-male group located at the Graafwater site,including all age-sex classes, were observed in the field by telescope, for atotal of 102 hours. All individuals were observed to predominantly displaymaintenance behavioural act systems, however, agonistic act systemswere also observed. Aggression levels were determined for the respectiveagonistic behavioural acts observed. Males were highly aggressive anddisplayed the most aggression (67.42 %). Females and sub-adultsdisplayed aggression for 34.97 % and 37.75 % of the total observationtime, respectively. Juveniles did not display aggression at all. Matingbehaviour was also observed and described. An ethogram was thusestablished for the first time for C. cataphractus, and was compared to theethograms available for a few other cordylids.The spatial distribution of individuals within a population has animportant impact on the social structure that ensues. Living in a groupimposes several pressures on the individual and competition for mates isone. The main aim of the study was to determine the space-use of all theindividuals included in a multi-male Cordylus cataphractus group (n = 55),to elaborate on the mating system. Specific focus was on the adult malesand females of the multi-male group, because, ultimately, the manner inwhich individuals, particularly the adult males and females, utilise space,determines the mating system. The mating system is an important aspectof social structure. A two-dimensional grid pattern was delineated at afree-living, multi-male group's crevice, situated at the Graafwater studysite, to be able to plot the position of each individual during observations.All marked individuals, that were visible, were scanned through atelescope and their respective positions were recorded at 30-minuteintervals. Arcview 3.2 Geographical Information Software was used tocreate a computerised model replicate of the two-dimensional grid patternat the crevice, and to graphically depict the recorded positions for eachindividual. The space-use of males overlapped greatly with the space-useof females (66.12 ± 31.81 %), but a 0 % overlap in space-use was observedamong adult males. The space-use of sub-adults and juveniles overlappedhighly among one another, as well as with the space-use of adult malesand females. The results showed conclusively that adult male C.cataphractus are territorial, defending specific sites at the crevice. Theterritory of each male included in the multi-male group incorporated atleast one female. The space-use of several females incorporated thespace-use of two or more males. Males were observed to mate with one ormore females, and one female was observed to mate with two differentmales on more than one occasion. Thus the evidence strongly suggests that C. cataphractus males display typical territorial polygyny whereasfemales may be promiscuous.

[发布机构] Stellenbosch University